1. Field of the Invention
The present invention relates to a method of polycrystallizing an amorphous silicon film by using a laser light, and to a method of improving crystallinity of polycrystalline silicon film by using a laser light. Also, the present invention relates to a thin film transistor using as an active layer the polycrystalline silicon film obtained by these methods, and to a semiconductor device using the thin film transistor.
2. Description of Related Art
In recent years, researches have been enthusiastically promoted on lowering temperature in manufacturing process of a semiconductor device, in particular, a thin film transistor (hereinafter, referred to as TFT). The main reason for this is that a need for forming a TFT on an insulating substrate such as glass which is inexpensive and is rich in processibility has been arisen. Also from the view point of aiming at a further minute device and a further multi-layered device, the lowering temperature in manufacturing process of a TFT is required.
In a manufacturing process of a high-performance TFT, a step is necessary of crystallizing an amorphous component in a semiconductor material, or an amorphous semiconductor material. For such a purpose, thermal annealing has conventionally been employed. When silicon is used as a semiconductor material, an amorphous component is crystallized by annealing at a temperature of 600xc2x0 C. to 1100xc2x0 C. for 0.1 to 48 hours, or for more than 48 hours.
Such thermal annealing as the above takes shorter processing time as the temperature rises higher. However, it is almost utterly ineffective when the temperature is 500xc2x0 C. or lower. Accordingly, from the view point of lowering temperature in manufacturing process, it is necessary to replace the thermal annealing step with other measures. When a glass substrate is used as a substrate in particular, since the heat resistant temperature of the glass substrate is about 600xc2x0 C., measures comparable to the above thermal annealing has been required when the temperature is lower than the heat resistant temperature.
As a way to fulfill the requirement mentioned above, polycrystallization of an amorphous component through irradiation of a semiconductor material with a laser light has recently attracted attention. Thermal annealing by irradiation of laser light can apply high energy comparable to the thermal annealing restrictedly to a desired portion, and hence has an advantage that not an entire substrate needs to be subjected to the heat of high temperature.
As to irradiation of laser light, approximately two methods have been proposed.
The first method uses continuous-wave laser and is a method of irradiating a beam like a spotlight to a semiconductor material. This is a method of polycrystallizing the semiconductor material utilizing the fact that the semiconductor material are slowly solidified after it is melted owing to difference in energy distribution within a beam and moving of the beam.
The second method is one that utilizes the fact that a crystal growth proceeds when a semiconductor material is instantaneously melted and is solidified by irradiating a laser pulse of large energy onto the semiconductor substrate using a pulse-generating laser apparatus such as an excimer laser apparatus.
A problem in the first method is that the process takes much time. This is because the size of the beam spot is several mm square at most, for having limitations in the maximum energy of the continuous-wave laser.
The second method makes a trial for employing a way to xe2x80x9cscanxe2x80x9d relatively to the substrate with a laser light the shape of which is changed into a linear one and which has a length longer than the substrate to be processed. With employment of such a way, the throughput can be significantly improved. The term xe2x80x9cscanxe2x80x9d here means to irradiate linear laser lights so as to overlap a little with one another.
However, the above technique of irradiating linear pulse laser lights so as to overlap a little with one another will generate linear stripes on the surface of the semiconductor material irradiated with laser. These stripes considerably affects a device formed on the semiconductor material, or a device to be formed later. Particularly, when a plurality of elements are formed on the substrate and every element has to have a uniform characteristic, the stripes become a serious problem. In such a case, the characteristic is uniform in each stripe pattern, but varies between the stripes that are different from each other.
In this way, uniformity in irradiation effect matters even in the annealing method using linear laser lights. High uniformity here designates that similar device characteristics is observed in a device formed in any portion on the substrate. To enhance uniformity means that crystallinity of a semiconductor material is unified.
Then, an excimer laser of large output has been developed lately, which is capable of annealing a large area with a single shot. When using this excimer laser of large output, amorphous silicon in a large area may be polycrystallized all at once. It has been proved that also the film quality of the polycrystallized silicon film is uniform to a certain degree within the plane.
Here, as a conventional example, a schematic top view illustrating a case where this excimer laser of large output is used in manufacturing an active matrix type liquid crystal display device is shown in FIG. 39.
In FIG. 39, reference numeral 3500 denotes a substrate; 3501 and 3505, active matrix circuits; 3502 and 3506, source driver circuits; 3503, 3504, 3507 and 3508, gate driver circuits. Reference numerals 3509 to 3512 denote irradiated regions with excimer laser light of large output, and an amorphous silicon film in the respective regions is polycrystallized with one shot or plural shots of the laser light. Thus, in this conventional example, the laser light is irradiated onto all the amorphous silicon films on the entire substrate by three times shifting, relatively to the substrate, of the laser light. It should be noted that although laser light irradiation regions 3509 to 3512 are shown in a pattern different from each other, for convenience""s sake in description, the same laser light is irradiated onto these regions.
It is readily understood here that irradiation of the laser light is carried out plural times onto repeatedly laser light irradiation regions, which are denoted by reference numerals 3513 to 3517. For instance, laser light is irradiated twice or more onto the region 3513, and four or more times onto the region 3517. It has been found that characteristic of polycrystalline silicon film is different when the number of irradiation time of the laser light is different, and therefore in such a conventional example, variation in characteristic of the polycrystalline silicon film is generated within the substrate surface. In this conventional example, the uniformity within the plane of the polycrystalline silicon film is thus cannot be obtained even when using the excimer laser of large output. As a result, though the throughput may be increased as compared to the case using a linear laser, problems are still remained as to the uniformity within the plane of polycrystalline silicon.
The present invention has been made in view of the above, and therefore an object of the invention is to provide a method of manufacturing a thin film transistor, in which when polycrystallizing an amorphous semiconductor film using a laser light, or when crystallinity of a semiconductor film is improved using a laser light, uniformity in the polycrystalline silicon film used for a thin film transistor in the substrate surface is realized to prevent variations in characteristic of the thin film transistor that uses the polycrystalline silicon film as an active layer and to enhance the throughput. Also, it is an object of the present invention to provide a high-performance semiconductor device using a thin film transistor fabricated by the manufacturing method.
In order to attain the above objects, reference is made to FIG. 1. FIG. 1 shows laser light irradiation regions when polycrystallizing an amorphous semiconductor film using excimer laser of large output in accordance with the present invention. In FIG. 1, as an example of a semiconductor device using a thin film transistor fabricated by a method of the present invention, a liquid crystal display device of active matrix is shown. It is to be noted that in this specification, although description is made of a case where silicon is used as an amorphous semiconductor film, the amorphous semiconductor film to be used is not limited to this but a film of an amorphous silicon germanium or the like may be used.
Reference numeral 100 denotes a substrate; 101 and 105, active matrix circuits; 102 and 106, source driver circuits; 103, 104, 107 and 108, gate driver circuits. In the method shown in FIG. 1, two active matrix substrates for an active matrix type liquid crystal display device can be obtained.
Reference numeral 109 to 112 denote laser light irradiation regions, and an amorphous silicon film in the respective regions is polycrystallized with one shot or plural shots of the laser light. Distances (gaps) denoted by xe2x80x9cA1xe2x80x9d and xe2x80x9cB1xe2x80x9d are distances (gaps) between the adjacent laser light irradiation regions, respectively. Also, reference numeral 113 denotes a laser light non-irradiation region to which the laser light is not irradiated.
As a process, the amorphous silicon film is irradiated with a laser light to be polycrystallized and is patterned, and, thereafter, the active matrix circuits, source driver circuits and gate driver circuits are formed. However, here for convenience""s sake in description, the laser light irradiation regions, and the active matrix circuits, source driver circuits and gate driver circuits which are to be formed later are shown in the same drawing.
In the method of polycrystallizing an amorphous silicon film according to the present invention, as shown in FIG. 1, laser light irradiation regions of large output do not overlap with one another. Different distances (gaps) xe2x80x9cA1xe2x80x9d and xe2x80x9cB1xe2x80x9d between different laser light irradiation regions are determined depending on a pixel pitch of the active matrix circuit or dimension of a TFT, dimension of a TFT of the driver circuit or the like, respectively. The circuits are designed so that regions defined by different distances (gaps) xe2x80x9cA1xe2x80x9d and xe2x80x9cB1xe2x80x9d between different laser light irradiation regions, in other words, regions to which the laser light is not irradiated (the laser light non-irradiation region 113) do not form active layers of thin film transistors constituting the active matrix circuit, driver circuit and other peripheral circuits.
In FIG. 1, portions denoted by xcex11 and xcex21 are the active matrix circuit and source driver circuit, respectively, and xcex11 and xcex21 represent portions including boundaries between a laser light irradiation region and laser light non-irradiation region. FIG. 10 is an enlarged view of the portion xcex11 and FIG. 11 is an enlarged view of the portion xcex21.
In FIG. 10, reference numeral 1001 denotes an active layer of a pixel TFT made of polycrystalline silicon, 1002 denotes first wirings and 1003 denotes second wirings. The first wirings 1002 function as the gate electrodes of the active layers in thin film transistors. It is to be noted that for convenience""s sake in description, pixel electrodes, interlayer insulating films or the like are omitted. PX is a pixel pitch in a direction of the X axis (row) and PY is a pixel pitch in a direction of the Y axis (column). SX is the length of the active layer in a direction of the X axis and SY is the length of the active layer in a direction of the Y axis. It is to be noted that in FIG. 10, triple gate type TFTs are used for the pixel TFTs, but single gate TFTs, double gate TFTs or TFTs other than these may be used. In any case, the length of the active layer in a direction of the X axis is designated by SX, and the length of the active layer in a direction of the Y axis is designated by SY. Portions painted out with black in the drawing illustrate portions in each of which the active layers and the second wiring layers, or the first wirings and the second wiring layers are brought into contact (are connected) with each other. What denoted by 1004 which are parts of the first wirings 1002 are formed to ensure the flatness between the wirings and the active layers.
It can be understood from FIG. 10 that the active layer of the thin film transistor does not enter into the laser light non-irradiation region 113. In other words, the active layer does not present in the laser light non-irradiation region 113 which is defined by distance (gap) xe2x80x9cA1xe2x80x9d (and distance xe2x80x9cB1xe2x80x9d) between the laser light irradiation region 111 and the laser light irradiation region 112. Therefore, it can be understood that the laser light non-irradiation region 113, i.e., a region that is not polycrystallized is not used as the active layer of the thin film transistor. When expressing this condition with PX, SX and A1, the following is established:
PXxe2x88x92SX greater than A1
Next, reference is made to FIG. 11. In the enlarged view of the portion xcex21 in FIG. 11, there is shown an inverter circuit within the source driver circuit 106. Reference numerals 1101 and 1102 denote the active layers of the thin film transistors made of polycrystalline silicon, and to the source region and drain region of each active layer, N type impurities and P type impurities are added. Reference numerals 1103 and 1104 denote first wirings and the wiring 1103 functions as a gate electrode of the active layer in the thin film transistor. A second wiring is denoted by 1105. Also in here, an interlayer insulating film or the like is omitted for convenience""s sake in description. Portions painted out with black in the drawing illustrate portions in each of which the active layer and the second wiring layer, or the first wiring and the second wiring layer are brought into contact (are connected) with each other.
It can be understood from FIG. 11 that the active layers 1101 and 1102 do not enter into the laser light non-irradiation region 113. In other words, the active layers 1101 and 1102 do not present in the laser light non-irradiation region 113 which is defined by distance (gap) xe2x80x9cA1xe2x80x9d (and distance xe2x80x9cB1xe2x80x9d) between the laser light irradiation region 111 and the laser light irradiation region 112. Therefore, it can be understood that the laser light non-irradiation region 113, i.e., a region that is not polycrystallized is not used again here as the active layers 1101 and 1102.
With employment of the above method using the laser light, improving crystallinity of a semiconductor film may also be possible. In this case also, film quality of a semiconductor film after irradiation with laser light is different between the laser light irradiation region and the laser light non-irradiation region. This is because crystallinity of the semiconductor film is improved by irradiating a laser light to the semiconductor film, thereby improving film quality. It is to be noted that all the methods using laser light which will be described hereinbelow may be adapted for improving crystallinity of this semiconductor film. Also, another method of the present invention to be described below can be adapted for improving crystallinity.
In this specification, a semiconductor film that is the subject of the irradiation with laser light may sometimes called an xe2x80x9cinitial semiconductor filmxe2x80x9d. This xe2x80x9cinitial semiconductor filmxe2x80x9d refers to as an xe2x80x9camorphous semiconductor film or amorphous semiconductor film partially including a crystalline componentxe2x80x9d, if it is before crystallization, and if before improving crystallinity, as a xe2x80x9ccrystalline semiconductor film or crystalline semiconductor film partially including an amorphous componentxe2x80x9d. Further, the term xe2x80x9chighly crystallized semiconductor filmxe2x80x9d may be used in this specification. This xe2x80x9chighly crystallized semiconductor filmxe2x80x9d designates a xe2x80x9cfilm with improved crystallinity or semiconductor film with reduced defect in grainxe2x80x9d.
Next, reference is made to FIG. 2. FIG. 2 shows laser light irradiation regions when polycrystallizing an amorphous silicon film using excimer laser of large output in accordance with the present invention. FIG. 2 shows a liquid crystal display device of active matrix type as an example of a semiconductor device having a thin film transistor that uses a polycrystalline silicon film manufactured by the method of the present invention.
Reference numeral 200 denotes a substrate; 201, an active matrix circuit; 202 and 203, source driver circuits; 204 and 205, gate driver circuits. Reference numerals 206 to 209 denote laser light irradiation regions, and an amorphous silicon film in the respective regions is polycrystallized with one shot or plural shots of the laser light. Distances denoted by xe2x80x9cA2xe2x80x9d and xe2x80x9cB2xe2x80x9d are distances between the adjacent laser light irradiation regions, respectively. Reference numeral 210 denotes a laser light non-irradiation region to which the laser light is not irradiated. In FIG. 2, one active matrix circuit of an active matrix type liquid crystal display device is manufactured from the substrate 200.
As a process, the amorphous silicon film is irradiated with a laser light to be polycrystallized and is patterned, and, thereafter, the active matrix circuit, source driver circuits and gate driver circuits are formed. However in FIG. 2, for convenience""s sake in description as in FIG. 1, the laser light irradiation regions, and the active matrix circuit, source driver circuits and gate driver circuits are shown in the same drawing.
In the method of polycrystallizing an amorphous silicon film according to the present invention, as shown in FIG. 2, laser light irradiation regions of large output do not overlap with one another. Distances (gaps) xe2x80x9cA2xe2x80x9d and xe2x80x9cB2xe2x80x9d between laser light irradiation regions are determined depending on a pixel pitch of the active matrix circuit or dimension of a pixel TFT, dimension of a TFT of the driver circuit or the like, respectively. The circuit is designed so that regions defined by distances (gaps) xe2x80x9cA2xe2x80x9d and xe2x80x9cB2xe2x80x9d between laser light irradiation regions, in other words, regions to which the laser light is not irradiated (the laser light non-irradiation region 210) do not form an active layer of thin film transistor.
In FIG. 2, portions denoted by xcex12, xcex22 and xcex32 are the active matrix circuit, source driver circuit and gate driver circuit, respectively, and xcex12, xcex22 and xcex32 represent portions including boundaries between a laser light irradiation region and laser light non-irradiation region. FIG. 12 is an enlarged view of the portion xcex32. As to the portions denoted by xcex12 and xcex22, since they are the same as the portions xcex11 and xcex21 mentioned above, please refer the description on those.
Reference is made to FIG. 12. Shown in FIG. 12 is a buffer circuit in a gate driver circuit 204. Reference numerals 1201 and 1202 denote the active layers of the thin film transistors made of polycrystalline silicon, and to the source region and drain region of each of the active layers 1201 and 1202, impurities for giving P type and impurities for giving N type are added. Reference numerals 1203 and 1204 denote first wirings and 1205 denotes second wirings. The first wirings 1203 function as the gate electrodes of the thin film transistors. Also in here, an interlayer insulating film or the like is omitted for convenience""s sake in description. Portions painted out with black in the drawing illustrate, as in FIGS. 9 and 10, portions in each of which the active layers and the second wirings, or the first wirings and the second wirings are brought into contact (are connected) with each other.
It can be understood from FIG. 12 that the active layers 1201 and 1202 do not enter into the laser light non-irradiation region 210. In other words, the active layers 1201 and 1202 do not present in the not-irradiated region 210 with laser light which is defined by the interval xe2x80x9cB2xe2x80x9d (and interval xe2x80x9cA2xe2x80x9d) between the laser light irradiation region 206 and the laser light irradiation region 208. Therefore, it can be understood that the laser light non-irradiation region 210, i.e., a region that is not polycrystallized is not used as the active layer.
Now, supplementary description will be made on the portion xcex12 in FIG. 2. In the active matrix circuit shown in FIG. 2, a pixel pitch in a direction of the X axis (row) is given as PX; a pixel pitch in a direction of the Y axis (column) as PY; the length of the active layer in a direction of the X axis as SX; and the length of the active layer in a direction of the Y axis as SY. In this case, when expressing conditions that fulfill the method of the present invention with PX, SX, A2 and B2, the following are established:
PXxe2x88x92SX greater than A2
PYxe2x88x92SY greater than B2
Therefore, in the method of polycrystallizing an amorphous silicon film in accordance with present invention, a laser light non-irradiation region is not used for the active layer of a thin film transistor that constitutes an active matrix circuit, source driver circuit, gate driver circuit or other peripheral circuit. Accordingly, only a semiconductor film that has a uniform characteristic is used for the active layer of a thin film transistor.
Next, reference is made to FIG. 3. FIG. 3 illustrates one of systems for polycrystallizing an amorphous silicon film of the present invention shown in FIG. 1. As to parts in FIG. 3 which uses the same reference numerals as that of FIG. 1, please refer the description of FIG. 1.
In FIG. 3, reference numeral 301 denotes an amorphous silicon film formed on a substrate. Reference numeral 302 denotes a laser light of large output, and a laser body and an optical system are omitted for convenience""s sake in description of the drawing. An excimer laser of large output is suitable for the laser body. Reference numeral 303 denotes a polycrystalline silicon film and the drawing illustrates a state in which an amorphous silicon in the region irradiated with the laser light is polycrystallized. Reference numeral 304 denotes a stage, on which the substrate 100 is set. The stage 304 is moved by a control device 305 for stage X position and a control device 306 for stage Y position. A margin for error of stop position of the stage 304 is about 0.04 xcexcm. By moving the stage 304, laser light irradiation region 302 may be controlled with high accuracy.
Alternatively, laser light irradiation position may be arranged to be movable and the X position and Y position of laser light may be controlled since it is sufficient that the laser light 302 and the substrate 100 are moved relatively to each other. Further, both laser light and substrate (i.e., stage) may be movable in position.
In the case shown in FIG. 3, the stage 304 shifts its position three times to polycrystallize substantially the entire surface of the amorphous silicon film 301 formed on the substrate 100. As mentioned in the description of FIG. 1, laser light is irradiated while spacing out the film by the distances (gaps) xe2x80x9cA1xe2x80x9d and xe2x80x9cB1xe2x80x9d, which causes a region that is not irradiated with laser light.
Subsequently, reference is made to FIG. 4. FIG. 4 illustrates one of systems for polycrystallizing an amorphous silicon film of the present invention shown in FIG. 1. Difference between this system and the system shown in FIG. 3 resides in a point that the area of a laser light 401 introduced by a laser optical system is widened toward traveling direction of the laser light. In this case also, a polycrystalline silicon film where inequality within the plane is suppressed as possible can be obtained by controlling with high accuracy the relative positions of the stage and the laser light.
Reference is then made to FIG. 5. FIG. 5 illustrates one of systems for polycrystallizing an amorphous silicon film of the present invention shown in FIG. 1. Difference between this system and the system shown in FIG. 4 resides in a point that the area of a laser light 501 introduced by a laser optical system is narrowed toward traveling direction of the laser light. In this case also, a polycrystalline silicon film where inequality within the plane is suppressed as possible can be obtained by controlling with high accuracy the relative positions of the stage and the laser light.
Next, reference is made to FIG. 6. FIG. 6 illustrates one of systems for polycrystallizing an amorphous silicon film of the present invention shown in FIG. 1. Difference between this system and the system shown in FIG. 1 resides in to control the area of the laser light irradiated to an amorphous silicon film by guiding through a slit 602 a laser light 601 introduced by a laser optical system. In this case also, a polycrystalline silicon film where inequality within the plane is suppressed as possible can be obtained by controlling with high accuracy the relative positions of the stage and the laser light.
Reference is subsequently made to FIG. 7. FIG. 7 illustrates one of systems for polycrystallizing an amorphous silicon film of the present invention shown in FIG. 1. Difference between this system and the system shown in FIG. 6 resides in a point that the area of a laser light 701 introduced by a laser optical system is narrowed toward traveling direction of the laser light. It is possible to control the area of the laser light irradiated to an amorphous silicon film by guiding through a slit 702 the laser light 701 introduced by a laser optical system. In this case also, a polycrystalline silicon film where inequality within the plane is suppressed as possible can be obtained by controlling with high accuracy the relative positions of the stage and the laser light.
Incidentally, also in the system shown in FIG. 4, the area of the laser light may be controlled by using a slit as illustrated in FIGS. 6 and 7.
Further, systems shown in FIGS. 3 to 7 are for polycrystallizing an amorphous silicon film of the present invention shown in FIG. 1, but, needless to say, may be utilized also as systems for polycrystallizing an amorphous silicon film of the present invention shown in FIG. 2.
Next, reference is made to FIG. 8. FIG. 8 illustrates a method of polycrystallizing an amorphous silicon film of the present invention in the case that larger substrate is employed. Shown in FIG. 8 is a liquid crystal display device of active matrix type as an example of a semiconductor device having a thin film transistor that uses a polycrystalline silicon film manufactured by a method of the present invention. Reference numeral 800 denotes a substrate; 801, an active matrix circuit; 802, source driver circuit; 803 and 804, gate driver circuits. Reference numerals 805 and 816 denote laser light irradiation regions, and an amorphous silicon film in the respective regions is polycrystallized with one shot or plural shots of the laser light. In the drawing, distances (gaps) denoted by xe2x80x9cA3xe2x80x9d, xe2x80x9cA4xe2x80x9d and xe2x80x9cA5xe2x80x9d, and xe2x80x9cB3xe2x80x9d and xe2x80x9cB4xe2x80x9d are distances (gaps) between the adjacent laser light irradiation regions, respectively. To a portion denoted by 817, the laser light is not irradiated. Also in the case that such a relatively large substrate is handled, distances (gaps) denoted by xe2x80x9cA3xe2x80x9d, xe2x80x9cA4xe2x80x9d and xe2x80x9cA5xe2x80x9d, and xe2x80x9cB3xe2x80x9d and xe2x80x9cB4xe2x80x9d are determined depending on a pixel pitch of the active matrix circuit or dimension of a pixel TFT, dimension of a TFT of the driver circuit or the like, respectively. The circuit is designed so that the laser light non-irradiation region does not form the active layer of the thin film transistor. See FIGS. 10, 11 and 12, respectively, as to the positional relationship between the laser light non-irradiation region and the active matrix circuit, between the laser light non-irradiation region and the source driver circuit, and between the laser light non-irradiation region and the gate driver circuit.
Subsequently, reference is made to FIG. 9. FIG. 9 shows one of systems for polycrystallizing an amorphous silicon film of the present invention in the case that the substrate shown in FIG. 8 is used. In FIG. 9, reference numeral 901 denotes an amorphous silicon film formed on a substrate. Reference numeral 902 denotes a laser light of large output, and a laser body and an optical system are omitted for convenience""s sake in description of the drawing. An excimer laser of large output is suitable for the laser body. Reference numeral 903 denotes a polycrystalline silicon film and the drawing illustrates a state in which an amorphous silicon in the region irradiated with the laser light is polycrystallized. Reference numeral 904 denotes a stage, on which a substrate 800 is set. The stage 904 is moved by a control device 905 for stage X position and a control device 906 for stage Y position. A margin for error of step position of the stage 904 is about 0.04 xcexcm. By moving the stage 904, laser light irradiation region 902 may be controlled with high accuracy.
Alternatively, laser light irradiation position with laser light may be arranged to be movable and the X position and Y position of laser light may be controlled since it is sufficient that the laser light 902 and the substrate 800 are moved relatively to each other. Further, both laser light and substrate (i.e., stage) may be movable in position.
In the case shown in FIG. 9, the stage 904 shifts its position eleven times to polycrystallize substantially the entire surface of the amorphous silicon film 901 formed on the substrate 800. As mentioned in the description of FIG. 1, laser light is irradiated while spacing out the film by the distances (gaps) xe2x80x9cA3xe2x80x9d, xe2x80x9cA4xe2x80x9d and xe2x80x9cA5xe2x80x9d, and xe2x80x9cB3xe2x80x9d and xe2x80x9cB4xe2x80x9d, which causes a region 817 that is not irradiated with laser light. The circuit is designed so that the this laser light non-irradiation region 817 is not used for the active layer of the thin film transistor. That is already described above.
The laser lights shown in FIGS. 4 to 7 may be used for the laser light 902.
Next, FIG. 13 illustrates another method of polycrystallizing an amorphous silicon film using excimer laser of large output in accordance with the present invention. FIG. 13 shows regions irradiated with laser light when polycrystallizing an amorphous silicon film in accordance with the present invention. Shown in FIG. 13 is an active matrix type liquid crystal display device as an example of a semiconductor device having a thin film transistor that uses a polycrystalline silicon film manufactured by a method of the present invention.
Reference numeral 1300 denotes a substrate; 1301 and 1305, active matrix circuits; 1302 and 1306, source driver circuits; 1303, 1304, 1307 and 1308, gate driver circuits. Reference numerals 1309 to 1312 denote laser light irradiation regions, and an amorphous silicon film in the respective regions is polycrystallized with one shot or plural shots of the laser light. In the method shown in FIG. 13, there partially exist end portions of adjacent irradiated regions, to which laser light is irradiated, overlap with each other (overlapping laser light irradiation regions 1313 to 1317). Lengths denoted by xe2x80x9cC1xe2x80x9d and xe2x80x9cD1xe2x80x9d in FIG. 13 are respectively lengths of regions where adjacent regions irradiated with laser light overlap with each other.
As a process, the amorphous silicon film is irradiated with a laser light to be polycrystallized and is patterned, and, thereafter, the active matrix circuits, source driver circuits and gate driver circuits are formed. However, here for convenience""s sake in description, the laser light irradiation regions, and the active matrix circuits, source driver circuits and gate driver circuits are shown in the same drawing. Though the irradiated regions 1309 to 1312 with laser light are shown in hatching patterns different from one another, equal laser light is irradiated onto each region.
In the method shown in FIG. 13, there are overlapping laser light irradiation regions 1313 to 1317, which means that there are regions different from one another in characteristic of a silicon film that is irradiated with laser light to be polycrystallized. In the method of FIG. 13, lengths xe2x80x9cC1xe2x80x9d and xe2x80x9cD1xe2x80x9d of the overlapping laser light irradiation regions 1313 to 1317 which are regions different from one another in film quality of the polycrystallized silicon film are determined depending c)n a pixel pitch of the active matrix circuit, dimension of a TFT of the driver circuit or the like, respectively. That is, the circuit is designed so that the overlapping laser light irradiation regions 1313 to 1317 do not form an active layer of the thin film transistor.
In FIG. 13, portions denoted by xcex41 and xcex51 are respectively the active matrix circuit region and the source driver region, and xcex41 and xcex51 denote portions including the overlapping laser light irradiation regions 1313 to 1317. FIG. 17 is an enlarged view of the portion xcex41 and FIG. 18 is an enlarged view of the portion xcex51.
Reference is made to FIG. 17. In FIG. 17, reference numeral 1701 denotes an active layer of a thin film transistor made of polycrystalline silicon, 1702 denotes first wirings and 1703 denotes second wirings. The first wirings 1702 function as the gate electrode of the active layer in the thin film transistor. Incidentally, for convenience""s sake in description, a pixel electrode, interlayer insulating film or the like is omitted. PX is a pixel pitch in a direction of the X axis (row) and PY is a pixel pitch in a direction of the Y axis (column). SX is the length of the active layer in a direction of the X axis and SY is the length of the active layer in a direction of the Y axis.
It can be understood from FIG. 17 that the active layer of the thin film transistor does not enter into the overlapping laser light irradiation region 1313. In other words, the active layer does not present in the overlapping laser light irradiation region 1313 which is defined by the length xe2x80x9cC1xe2x80x9d of the region where the laser light irradiation region 1311 and the laser light irradiation region 1312 overlap with each other. Therefore, it can be understood that the overlapping laser light irradiation region 1313 is not used as the active layer of the thin film transistor. The active layer of the thin film transistor thus does not employ polycrystalline silicon films different in characteristic. When expressing this condition with PX, SX and C1, the following is established:
PXxe2x88x92SX greater than C1
Next, reference is made to FIG. 18. In the enlarged view of the portion xcex51 shown in FIG. 13, there is shown an inverter circuit within the source driver circuit 1306. Reference numerals 1801 and 1802 denote the active layers of the thin film transistor made of polycrystalline silicon, and to the source region and drain region of each active layer, N type impurities and P type impurities are added. Reference numerals 1803 and 1804 denote first wirings and the wiring 1803 functions as a gate electrode of the active layer in the thin film transistor. A second wiring is denoted by 1805. Also in here, an interlayer insulating film or the like is omitted for convenience""s sake in description. Portions painted out with black in the drawing illustrate portions in each of which the active layer and the second wiring layer, or the first wiring and the second wiring layer are brought into contact (are connected) with each other. It can be understood from FIG. 18 that the active layers 1801 and 1802 do not enter into the overlapping irradiated region 1313 with laser light. In other words, the active layers 1801 and 1802 do not present in the overlapping laser light irradiation region 1313 which is defined by the length xe2x80x9cC1xe2x80x9d (and length xe2x80x9cD1xe2x80x9d) of the region where the laser light irradiation region 1311 and the laser light irradiation region 1312 overlap with each other. Therefore, it can be understood that the silicon film of the overlapping laser light irradiation region 1313 is not used as the active layer of the thin film transistor. The active layer of the thin film transistor thus does not use polycrystalline silicon films different in characteristics.
Next, reference is made to FIG. 14. FIG. 14 shows laser light irradiation regions when polycrystallizing an amorphous silicon film using excimer laser of large output in accordance with the present invention. FIG. 14 shows an active matrix type liquid crystal display device as an example of a semiconductor device having a thin film transistor that uses a polycrystalline silicon film manufactured by a method of the present invention.
Reference numeral 1400 denotes a substrate; 1401, An active matrix circuit; 1402 and 1403, source driver circuits; 1404 and 1405, gate driver circuits. Reference numerals 1406 to 1409 denote laser light irradiation regions, and an amorphous silicon film in the respective regions is polycrystallized with one shot or plural shots of the laser light. In the method shown in FIG. 14, as illustrated in FIG. 13, there partially exist end portions of adjacent irradiated regions, to which laser light is irradiated, overlap with each other (overlapping irradiated regions 1410 to 1414 with laser light). Lengths denoted by xe2x80x9cC2xe2x80x9d and xe2x80x9cD2xe2x80x9d in FIG. 14 are respectively lengths of regions where adjacent regions irradiated with laser light overlap with each other.
As a process, the amorphous silicon film is irradiated with a laser light to be polycrystallized and is patterned, and, thereafter, the active matrix circuit, source driver circuits and gate driver circuits are formed. However in FIG. 14, for convenience""s sake in description as in FIG. 13, the laser light irradiation regions, and the active matrix circuit, source driver circuits and gate driver circuits are shown in the same drawing. Though the laser light irradiation regions 1406 to 1409 are shown in hatching patterns different from one another, equal laser light is irradiated on each region.
In the method shown in FIG. 14, there are overlapping laser light irradiation regions 1410 to 1414, which means that there are regions different from one another in characteristic of a silicon film that is irradiated with laser light to be polycrystallized. In the method of FIG. 14, lengths xe2x80x9cC2xe2x80x9d and xe2x80x9cD2xe2x80x9d of the overlapping laser light irradiation regions 1410 to 1414 which are regions different from one another in film quality of the polycrystallized silicon film are determined depending on a pixel pitch of the active matrix circuit, dimension of a pixel TFT, dimension of a TFT of the driver circuit or the like, respectively. That is, the circuit is designed so that the overlapping laser light irradiation regions 1410 to 1414 do not form an active layer of the thin film transistor.
In FIG. 14, portions denoted by xcex52, xcex42 and xcex62 are respectively the active matrix circuit, the source driver circuit and gate driver circuit, and xcex52, xcex42 and xcex62 denote portions including the overlapping laser light irradiation region 1410. FIG. 19 is an enlarged view of the portion xcex62. The portions xcex52 and xcex42 are the same as the portions xcex52 and xcex42 shown in FIGS. 17 and 18, and hence description is omitted here.
Reference is made to FIG. 19. Shown in FIG. 19 is a buffer circuit in a gate driver circuit 1404. Reference numerals 1901 and 1902 denote the active layers of the thin film transistors made of polycrystalline silicon, and to the source region and drain region of each of the active layers 1901 and 1902, impurities for giving P type and impurities for giving N type are introduced. Reference numerals 1903 and 1904 denote first wirings and 1905 denotes second wirings. The first wirings 1903 function as the gate electrodes of the thin film transistors. Also in here, an interlayer insulating film or the like is omitted for convenience""s sake in description. Portions painted out with black in the drawing illustrate portions in each of which the active layer and the second wirings, or the first wirings and the second wirings are brought into contact (are connected) with each other. It can be understood from FIG. 19 that the active layers 1901 and 1902 do not enter into the overlapping laser light irradiation region 1410. In other words, the active layers 1901 and 1902 do not present in the overlapping laser light irradiation region 1410 which is defined by the length xe2x80x9cD2xe2x80x9d of the region where the laser light irradiation region 1406 and the laser light irradiation region 1408 overlap with each other. The active layers 1901 and 1902 do not present in the overlapping laser light irradiation region 1410. Therefore, it can be understood that the silicon film of the overlapping laser light irradiation region 1410 is not used as the active layer of the thin film transistor. The active layer of the thin film transistor thus does not employ polycrystalline silicon films different in characteristic.
Now, supplementary description will be made of the portion xcex52 in FIG. 14. In the active matrix circuit shown in FIG. 14, a pixel pitch in a direction of the X axis (row) is given as PX; a pixel pitch in a direction of the Y axis (column) as PY; the length of the active layer in a direction of the X axis as SX; and the length of the active layer in a direction of the Y axis as SY. In this case, when expressing conditions that fulfill the method of the present invention with PX, PY, SX, SY, C2 and D2, the following is established:
xe2x80x83PXxe2x88x92SX greater than C2
PYxe2x88x92SY greater than D2
Next, reference is made to FIG. 15. FIG. 15 illustrates one of systems for polycrystallizing an amorphous silicon film of the present invention shown in FIG. 13. As to parts in FIG. 15 which uses the same reference numerals as in FIG. 13, see description on FIG. 13.
In FIG. 15, reference numeral 1501 denotes an amorphous silicon film formed on a substrate. Reference numeral 1502 denotes a laser light of large output, and a laser body and an optical system are omitted for convenience""s sake in description of the drawing. An excimer laser of large output is suitable for the laser body. Reference numeral 1503 denotes a polycrystalline silicon film and the drawing illustrates a state in which an amorphous silicon in the region irradiated with the laser light is polycrystallized. Reference numeral 1504 denotes a stage, on which the substrate 1300 is set. The stage 1504 is moved by a control device 1505 for stage X position and a control device 1506 for stage Y position. A margin for error of stop position of the stage 1504 is about 0.04 xcexcm. By moving the stage 1504, laser light irradiation region 1502 may be controlled with high accuracy.
Alternatively, laser light irradiation position may be arranged to be movable and the X position and Y position of laser light may be controlled since it is sufficient that the laser light 1502 and the substrate 1300 are moved relatively to each other. Further, both laser light and substrate (i.e., stage) may be movable in position.
The laser lights shown in the above FIGS. 4 to 7 may be used in this system shown in FIG. 15.
Next, reference is made to FIG. 16. FIG. 16 illustrates a method of polycrystallizing an amorphous silicon film of the present invention in the case that larger substrate is employed. Shown in FIG. 16 is a liquid crystal display device of active matrix type as an example of a semiconductor device having a thin film transistor that uses a polycrystalline silicon film manufactured by the method of the present invention. Reference numeral 1600 denotes a substrate; 1601, an active matrix circuit; 1602, a source driver circuit; 1603 and 1604, gate driver circuits. Reference numerals 1605 to 1616 denote laser light irradiation regions, and an amorphous silicon film in the respective regions is polycrystallized with one shot or plural shots of the laser light. In the drawing, lengths denoted by xe2x80x9cC3xe2x80x9d, xe2x80x9cC4xe2x80x9d and xe2x80x9cC5xe2x80x9d, and xe2x80x9cD3xe2x80x9d and xe2x80x9cD4xe2x80x9d are respectively lengths of portions where adjacent laser light irradiation regions overlap with each other. In the method shown in FIG. 16, there is a portion where a laser light irradiation region overlaps with an end portion of another laser light irradiation region (overlapping laser light irradiation regions, representatively, regions denoted by 1617 to 1619). The lengths denoted by xe2x80x9cC3xe2x80x9d, xe2x80x9cC4xe2x80x9d and xe2x80x9cC5xe2x80x9d, and xe2x80x9cD3xe2x80x9d and xe2x80x9cD4xe2x80x9d are respectively lengths of regions where adjacent laser light irradiation regions overlap with each other.
As a process, the amorphous silicon film is irradiated with a laser light to be polycrystallized and is patterned, end, thereafter, the active matrix circuit, source driver circuit and gate driver circuits are formed. However in FIG. 16, here for convenience""s sake in description as in FIGS. 13 and 14, the laser light irradiation regions, and the active matrix circuit, source driver circuit and gate driver circuits are shown in the same drawing. Though the laser light irradiation regions 1605 to 1616 are shown in hatching patterns different from one another, equal laser light is irradiated onto each region.
Also in the method of polycrystallizing an amorphous silicon film shown in FIG. 16, respective circuits, namely, the active matrix circuit 1601, source driver circuit 1602 and gate driver circuit 1603 are designed so that the silicon films of the overlapping laser light irradiation regions representatively denoted by 1617 to 1619 are not used as the active layers of thin film transistors that constitute those circuits. The lengths xe2x80x9cC3xe2x80x9d, xe2x80x9cC4xe2x80x9d and xe2x80x9cC5xe2x80x9d, and xe2x80x9cD3xe2x80x9d and xe2x80x9cD4xe2x80x9d may be equal with one another, or may be different from one another. The lengths xe2x80x9cC3xe2x80x9d, xe2x80x9cC4xe2x80x9d and xe2x80x9cC5xe2x80x9d, and xe2x80x9cD3xe2x80x9d and xe2x80x9cD4xe2x80x9d may be changed depending on how the circuit is designed. That is, also in the case that such a relatively large substrate is handled, the lengths xe2x80x9cC3xe2x80x9d, xe2x80x9cC4xe2x80x9d and xe2x80x9cC5xe2x80x9d, and xe2x80x9cD3xe2x80x9d and xe2x80x9cD4xe2x80x9d are determined depending on a pixel pitch of the active matrix circuit or dimension of a pixel TFT, dimension of a TFT of the driver circuit or the like, respectively. In addition, the circuit is designed so that the laser light non-irradiation region does not form the active layer of the thin film transistor. See FIGS. 17, 18 and 19, respectively, as to the positional relationship between the laser light non-irradiation region and the active matrix circuit, between the laser light non-irradiation region and the source driver circuit, and between the laser light non-irradiation region and the gate driver circuit.
Incidentally, the system for polycrystallizing an amorphous silicon film of the present invention shown in FIG. 16 is similar to one shown in FIG. 9.
Next, reference is made to FIG. 31. FIG. 31 illustrates the method of polycrystallizing an amorphous silicon film of the present invention shown in FIG. 1, in which, however, the laser light is irradiated so that a laser light irradiation region includes an end portion of the substrate. This method may be applied to methods described with reference to the accompanying figures other than FIG. 1.
Of the silicon films polycrystallized by methods shown in FIGS. 13 and 14, silicon films in laser light irradiation regions are usually not used for the active layer of the thin film transistor as described above. However, if laser light irradiation regions are shifted resulting that a silicon film of an overlapping laser light irradiation region is used for the active layer of the thin film transistor, it may in some cases operate as a thin film transistor without any trouble, though variations may be caused a little, and there is no fear of extreme decline in yield of the product.
It is needless to say that all the above described methods of polycrystallizing an amorphous silicon film may be used to improve crystallinity after thermal SPC (Solid Phase Crystallization) or SPC using catalytic elements. Namely, an xe2x80x9cinitial semiconductor filmxe2x80x9d may be irradiated with excimer laser light of large output to be crystallized to the higher extent.
The structure of the present invention will be described below.
According to a first aspect of the present invention, there is provided a method of manufacturing a thin film transistor comprising:
the first step of forming a semiconductor film on a substrate;
the second step of irradiating onto a part of the semiconductor film one shot or plural shots of laser light of 5 J or more in total energy and 100 nsec or more in pulse width to form a highly crystalized semiconductor film;
the third step of repeatedly performing the second step onto a part of the semiconductor film different from the part of the second step while shifting relative positions of the semiconductor film and the laser light to each other; and
the fourth step of forming a thin film transistor having as an active layer the highly crystallized semiconductor film.
According to a second aspect of the present invention, there is provided a method of manufacturing a thin film transistor comprising:
the first step of forming an initial semiconductor film on a substrate;
the second step of irradiating onto a part of the initial semiconductor film one shot or plural shots of laser light of 5 J or more in total energy and 100 nsec or more in pulse width to form a highly crystalized semiconductor film;
the third step of repeatedly performing the second step onto a part of the initial semiconductor film different from the part of the second step while shifting relative positions of the initial semiconductor film and the laser light to each other; and
the fourth step of forming a thin film transistor having as an active layer the highly crystallized semiconductor film.
According to a third aspect of the present invention, there is provided a method of manufacturing a thin film transistor comprising:
the first step of forming a semiconductor film on a substrate;
the second step of irradiating onto a part of the semiconductor film one shot or plural shots of laser light of 5 J or more in total energy and 100 nsec or more in pulse width to form a highly crystalized semiconductor film;
the third step of repeatedly performing the second step while shifting relative positions of the semiconductor film and the laser light to each other, and irradiating the laser light duplicately onto the part of the semiconductor film; and
the fourth step of forming a thin film transistor having as an active layer the highly crystallized semiconductor film.
According to a fourth aspect of the present invention, there is provided a method of manufacturing a thin film transistor comprising:
the first step of forming an initial semiconductor film on a substrate;
the second step of irradiating onto a part of the initial semiconductor film one shot or plural shots of laser light of 5 J or more in total energy and 100 nsec or more in pulse width to form a highly crystalized semiconductor film;
the third step of repeatedly performing the second step while shifting relative positions of the initial semiconductor film and the laser light to each other, and irradiating the laser light duplicately onto the part of the initial semiconductor film; and
the fourth step of forming a thin film transistor having as an active layer the highly crystallized semiconductor film.
According to a fifth aspect of the present inventions, there is provided a method of manufacturing a thin film transistor as set forth in the first or third aspect of the present invention, wherein the semiconductor film comprises a silicon film or a germanium film.
According to a sixth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the second or fourth aspect of the present invention, wherein the initial semiconductor film comprises a silicon film or a silicon germanium film.
According to a seventh aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the first, second of fifth aspect of the present invention, wherein a gap between the highly crystallized semiconductor films is about 10 xcexcm or less.
According to an eighth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the first or second aspect of the present invention, wherein a gap between the part of the semiconductor film and the different part thereof is about 10 xcexcm or less.
According to a ninth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in any one of the first through fourth aspects of the present invention, wherein only the highly crystallized semiconductor film is used as the active layer.
According to a tenth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in any one of the first through fourth aspects of the present invention, wherein the length of the part of the semiconductor film is about 10 xcexcm or less.
According to an eleventh aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in any one of the first through fourth aspects of the present invention, wherein the pulse width of the laser light is 200 nsec or more.
According to a twelfth aspect of the present invention, there is provided a method of manufacturing a thin film transistor comprising:
the first step of forming an amorphous semiconductor film on a substrate;
the second step of irradiating onto a part of the amorphous semiconductor film one shot or plural shots of laser light of 5 J or more in total energy and 100 nsec or more in pulse width;
the third step of repeatedly performing the second step onto a part of the amorphous semiconductor film different from the second step while shifting relative positions of the amorphous semiconductor film and the laser light to each other, to thereby form a polycrystalline semiconductor film; and
the fourth step of forming a thin film transistor having as an active layer the polycrystalline semiconductor film.
According to a thirteenth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the twelfth aspect of the present invention, wherein the amorphous semiconductor film comprises an amorphous silicon film or an amorphous silicon germanium film.
According to a fourteenth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the twelfth aspect of the present invention, wherein a gap between the polycrystalline semiconductor films is about 10 xcexcm or less.
According to a fifteenth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the twelfth aspect of the present invention, wherein a gap between the part of the amorphous semiconductor film and the different part thereof is about 10 xcexcm or less.
According to a sixteenth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the twelfth aspect of the present invention, wherein the pulse width of the laser light is 200 nsec or more.
According to a seventeenth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the twelfth aspect of the present invention, wherein among the amorphous semiconductor films, only the polycrystallized region is used as the active layer.
According to an eighteenth aspect of the present invention, there is provided a method of manufacturing a thin film transistor comprising:
the first step of forming an amorphous semiconductor film on a substrate;
the second step of irradiating onto a part of the amorphous semiconductor film one shot or plural shots of laser light of 5 J or more in total energy and 100 nsec or more in pulse width;
the third step of repeatedly performing the second step by irradiating the laser light onto a region that overlaps with the part of the amorphous semiconductor film, while shifting relative positions of the amorphous semiconductor film and the laser light to each other, to thereby polycrystallize substantially the entire region of the amorphous semiconductor film; and
the fourth step of forming a thin film transistor having as an active layer the polycrystalline semiconductor film.
According to a nineteenth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the eighteenth aspect of the present invention, wherein the amorphous semiconductor film comprises an amorphous silicon film or an amorphous silicon germanium film.
According to a twentieth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the eighteenth aspect of the present invention, wherein the length of the region that overlaps with the part of the amorphous semiconductor film is about 10 xcexcm or less.
According to a twenty-first aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the eighteenth aspect of the present invention, wherein the pulse width of the laser light is 200 nsec or more.
According to a twenty-second aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the eighteenth aspect of the present invention, wherein among the polycrystallized silicon film, only a region excluding the part of the amorphous silicon film is used as the active layer.
According to a twenty-third aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in any one of the first through fourth, twelfth and eighteenth aspects of the present invention, wherein the laser light is one obtained by the use of excimer laser units coupled with one another to form two, three or four tiers.
According to a twenty-fourth aspect of the present invention, there is provided a method of manufacturing a thin film transistor comprising:
the first step of forming an amorphous silicon film on a substrate;
the second step of irradiating onto a part of the amorphous semiconductor film a single shot of laser light with a total energy of 5 J or more to polycrystallize the amorphous silicon film;
the third step of repeatedly performing the second step to polycrystallize substantially the entire region of the amorphous silicon film; and
the fourth step of forming a thin film transistor having as an active layer the polycrystallized amorphous silicon film.
According to a twenty-fifth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the twenty-fourth aspect of the present invention, wherein a gap between the polycrystallized amorphous silicon films is about 10 xcexcm or less.
According to a twenty-sixth aspect of the present invention, there is provided a method of manufacturing a thin film transistor as set forth in the twenty-fourth aspect of the present invention, wherein among the amorphous silicon films, only the polycrystallized region is used as the active layer.
According to a twenty-seventh aspect of the present invention, there is provided a thin film transistor manufactured in accordance with a method as set forth in the twenty-fourth aspect of the present invention.